The planet, "e", in the famous system Gliese 581, in the constellation of Libra and 20.5 light years (192 trillion km or 119 trillion miles) away, is only about twice the mass of Earth. The team also refined the orbit of the planet Gliese 581 d, (coloured blue in image) first discovered in 2007, placing it well within the habitable zone, where liquid water oceans could exist.